1. Technical Field
The present disclosure relates to antennas and, more particularly, to electrosurgical devices with leaky-wave antenna assemblies suitable for use in tissue ablation applications.
2. Discussion of Related Art
Treatment of certain diseases requires the destruction of malignant tumors. Electromagnetic radiation can be used to heat and destroy tumor cells. Treatment may involve inserting ablation probes into tissues where cancerous tumors have been identified. Once the probes are positioned, electromagnetic energy is passed through the probes into surrounding tissue.
In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures that are slightly lower than temperatures normally injurious to healthy cells. Known treatment methods such as hyperthermia therapy, use electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells below the temperature at which irreversible cell destruction occurs. These methods involve applying electromagnetic radiation to heat, ablate and/or coagulate tissue. Microwave energy is sometimes utilized to perform these methods. Other procedures utilizing electromagnetic radiation to heat tissue also include coagulation, cutting and/or ablation of tissue.
Electrosurgical devices utilizing electromagnetic radiation have been developed for a variety of uses and applications. A number of devices are available that can be used to provide high bursts of energy for short periods of time to achieve cutting and coagulative effects on various tissues. There are a number of different types of apparatus that can be used to perform ablation procedures Typically, microwave apparatus for use in ablation procedures include a microwave generator, which functions as an energy source, and a microwave surgical instrument having an antenna assembly for directing the energy to the target tissue. The microwave generator and surgical instrument are typically operatively coupled by a cable assembly having a plurality of conductors for transmitting microwave energy from the generator to the instrument, and for communicating control, feedback and identification signals between the instrument and the generator.
Microwave energy is typically applied via antenna assemblies that can penetrate tissue. Several types of microwave antenna assemblies are known, such as monopole, dipole and helical. In monopole and dipole antenna assemblies, microwave energy generally radiates perpendicularly away from the axis of the conductor. A monopole antenna assembly includes a single, elongated conductor that transmits microwave energy. A typical dipole antenna assembly has two elongated conductors, which are linearly aligned and positioned end-to-end relative to one another with an electrical insulator placed therebetween. Helical antenna assemblies have two main modes of operation: normal mode (broadside) and axial mode (endfire). In the normal mode of operation, the field radiated by the helix is maximum in a perpendicular plane to the helix axis. In the axial mode, maximum radiation is along the helix axis.
A typical microwave transmission line assembly has a long, thin inner conductor that extends along a longitudinal transmission line axis and is surrounded by a dielectric material and is further surrounded by an outer conductor around the dielectric material such that the outer conductor also extends along the transmission line axis. In one variation of an antenna, the outer conductor is provided with a plurality of slots along a length of transmission line. This type of construction is typically referred to as a “leaky coaxial” or “leaky wave” antenna. A leaky wave antenna is basically a waveguiding structure constructed so as to “leak” power along the length of the guiding structure. In a leaky-wave antenna, as the microwave signal propagates inside the guiding structure (i.e., transmission line or coaxial cable), it “leaks” out through openings in the outer conductor, causing radiation.
Examples of leaky coaxial antennas include loose braid coaxial cables and slotted coaxial cables, which are sometimes used for communications applications such as, for example, transmitting and receiving signals within tunnels or buildings. A typical loose braid coaxial cable is shown in FIG. 1 and includes an inner conductor 120, an outer conductor 150 coaxially surrounding the inner conductor 120, and a dielectric material 140 separating the inner and outer conductors. The direction of the radiation pattern of the loose braid coaxial cable is indicated by the curved arrows in FIG. 1. An example of a slotted coaxial cable is illustrated in FIG. 2 and includes a central conductor 220, a cylindrical outer conductor 260, which is provided with a plurality of elongated slots 201A, 201B and 201C, and a dielectric material 240 separating the inner and outer conductors. In the slotted coaxial cable illustrated in FIG. 2, the slots 201A, 201B and 201C longitudinally extend along the longitudinal axis of the inner conductor 220. In the slotted coaxial cable shown in FIG. 3, a plurality of slots 301A, 301B and 301C are formed in the outer conductor 360 such that the longitudinal axis of each slot extends perpendicular to the longitudinal axis of the central conductor 320.
During certain procedures, it can be difficult to assess the extent to which the microwave energy will radiate into the surrounding tissue, making it difficult to determine the area or volume of surrounding tissue that will be ablated.